How many DOF are constrained 1

[SeasonLee]

For the figure attached, how many degrees of freedom are constrained by datum feature ‘E’ if it becomes a primary datum feature?

The answer is 5 DOF are constrained, why? Datum feature E is a Ø10 hole, its true geometric counterpart is a best fit gage pin, so for a cylindrical axis will constrain 4 DOF only according to the Fig. 4-3 of 2009 standard, why 5 DOF?
Thanks for the inputs

Season

 

[greenimi]

Quote:"Datum feature E is a Ø10 hole"

Datum fetaure E is a PATTERN of 2 holes ! (not a single hole).
My vote is 5 degrees of freedom.
Left only the transaltion along the axis

 

[greenimi]

And more than that, I would reference E at its MMC, for 58±0.3 positional callout.
So, would be pos. 0.4 with D primary and E(M) (AT MMC OR MMB/2009)

 

[3DDave]

The constrain 5, 3 very well and the other 2 very poorly.

All it takes is to imaging the part being on two horizontal parallel rods.

Shifting up or down is limited by either of the holes, and turning around either of the rods is limited by the fact the it is a pair of holes.

The part is still free to rotate about two other axes a large amount. If used as a primary datum feature, that amount of rotation would be allowed in establishing the orientation of the part in the DRF. That's why having the flat as a primary is a good idea, plus the flat also controls movement along the previously mentioned rods, which was the uncontrolled 6th degree of freedom.

 

[fsincox]

My guess is it works D (primary), E@MMC (secondary).
Frank

 

[SeasonLee]

Thanks for all comments, I didn't notice its a hole pattern (2X), my bad.

When a FOS datum feature is referenced at MMC, a datum shift is permissible, but I think even though a datum shift may be present, the part is still considered constrained.

Season

 

[Belanger]

I agree -- it's 5 DOF in theory. However, depending on the thickness of the part, the "wavering" aspect may not be adequately controlled, as Dave mentions.

FYI: Just in case this is a real print, the position tolerance on datum feature C needs a diameter symbol.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[3DDave]

JP,

Notice the A-B-C reference; A-B restricts all the degrees of freedom, so C is superfluous. Had it been A-C-B that would be different.

Did 2009 make MMC the default if not mentioned? I thought the material condition was required.

 

[SeasonLee]

Dave, good and interesting points.

Season

 

[Belanger]

Dave -- I wasn't stating whether a datum C is needed or not; that is irrelevant. (And, for all we know, it might have been used elsewhere on the drawing as a datum reference in a perfectly valid manner.)
My comment was simply that that feature control frame needs a diameter symbol.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[3DDave]

It was just a further observation - until your comment I hadn't looked much beyond the original question.

It's not that C is not usable, it's meaningless following A-B for B as RFS.